The present disclosure relates to an image sensor, and in particular, to a metal-oxide-semiconductor image sensor (CMOS CIS).
An image sensor is a semiconductor device configured to covert optical images into electrical signals. The image sensor may be classified into two types: a charge coupled device (CCD) type and a complementary metal-oxide-semiconductor (CMOS) type. In general, the CMOS-type image sensor may be called “CIS”. The CIS may include a plurality of two-dimensionally arranged pixels, each of which includes a photodiode (PD) that coverts incident light into an electrical signal.
As an integration density of the image sensor increases, a size of each pixel or photodiode in the image sensor becomes less and less. A photodiode may be strongly affected by a small variation in structure or external environment, and thus, the photodiode may suffer from low light sensitivity.